| The thesis describes several approaches to the preparation of CO 2 based polarity switchable solvents and their applications.; Two polar solvents (DMF and DMSO) were investigated as CO2 expanded solvents. The polarity of CO2 expanded solvents decreases as CO2 pressure increases, which was verified by the change in the maximum UV absorption wavelength of Nile red dye in these solvents. By pressurizing or releasing CO2 pressure, the polarity of these solvent systems was switched reversibly.; Amidines react with CO2 and water to form bicarbonate salts rather than the reported DBU-CO2 adduct. The reaction is completely reversible under certain conditions, and the switchable polarity was proven by the color change of Reichardt's solvatochromic dye. Amidines react with CO2 and alcohols to form carbamate ionic liquids, a new solvent system never reported before. By bubbling inert gas through these ionic liquids, the reaction can be completely reversed. Structures of alcohols and bases have a substantial effect on the properties of the ionic liquids. Alcohols with short linear alkyl chains generate more viscous ionic liquids.; Secondary amines react with CO2 to form carbamates. These carbamates are thermally unstable at high temperatures, which make the conversion reversible. Tertiary amines and related heterocyclic compounds do not react with CO2 for two reasons: they are not basic enough to form bicarbonates or adducts and they do not have acidic protons.; Several two-step reactions were designed as applications for these polarity switchable systems. However, no two-step reactions were demonstrated as successful. DBU is too reactive, which limits the applications of these switchable solvents. |
